Problems associated with fuel lubricity arose in the mid-1960's when a number of aviation fuel pump failures occurred. After considerable research, it was realized that advances in the refining of aviation turbine fuel had resulted in the almost complete removal of the naturally occurring lubricating components from the fuel. The removal of these natural lubricants resulted in the seizure of fuel pump parts. By the mid-1980's, it seemed likely that a similar problem was imminent in diesel fuel pumps. Fuel injection pump pressures had been steadily increasing while there was also a growing concern to reduce the sulfur content of the diesel fuel. The desire to reduce the sulfur content of the diesel fuel, in an effort to reduce pollution, required the use of more rigorous fuel refining processes. It was determined that as refining processes became more stringent, the naturally occurring oxygen containing compounds and polyaromatics which contribute to diesel fuel's inherent lubricity were eliminated. In response to these developments, a number of effective lubricity additives were developed for diesel fuels. These additives are now widely used to enhance the lubricity of highly refined, low sulfur diesel fuels.
Gasoline fuels are also becoming subject to compositional constraints, including restrictions on sulfur content, in an effort to reduce pollutants. The principle concern is the effect of sulfur on exhaust catalyst life and performance. The lubricity requirements of gasoline are somewhat lower than for diesel fuel since the majority of gasoline fuel injection systems inject fuel upstream of the inlet valves and thus operate at much lower pressures than diesel fuel pumps. However, as automobile manufacturers desire to have electrically powered fuel pumps within the fuel tanks, failure of the pumps can be expensive to repair. These problems are also likely to increase as injection systems become more sophisticated and the gasoline fuels become more highly refined.
Additional pump wear concerns have arisen with the introduction of vehicles having gasoline direct injection engines (GDI) since the fuel pumps for these vehicles operate at significantly higher pressures than traditional gasoline fuel pumps.
Another area subject to pump wear and failure is the use of submerged fuel pumps in gasoline or diesel fuel storage tanks. It is important to reduce the wear of these submerged pumps due to the difficulty of getting to these pumps for repair and maintenance.
Many commercially available gasoline fuels contain gasoline detergents such as polyisobutylene amine and polyether amine. These compounds are known to have a minor effect on the wear properties of the fuel. A growing number of commercially available gasoline fuels contain oxygenates, such as methyltertiarybutylether (MTBE). These oxygenates are known to increase rates of wear of fuel pump components as they have very high friction coefficients. In light of the desire for more highly refined fuels, lower sulfur content and oxygenation of the fuels, there is presently a need for lubricity improvers for hydrocarbon fuels in order to obtain acceptable fuel pump life. The present invention solves these problems by adding the reaction product of a carboxylic acid and at least one amine selected from the group consisting of guanidine, aminoguanidine, urea and thioruea to the fuel.
U.S. Pat. No. 3,655,560 to Andress, Jr. discloses fuels and lubricants containing aminoguanidine-based antioxidants. The basic teaching of this patent is that agents selected from ketimines of aminoguanidine, aldimines of ketimines of aminoguanidine and aldimines of amides of aminoguanidine are useful in inhibiting the oxidation of liquid hydrocarbon fuels and hydrocarbon lubricants. This patent does not address the lubricity issues of petroleum based fuels and the agents disclosed as useful antioxidants are not the same as the lubricity additives disclosed herein.
U.S. Pat. No. 4,536,189 to Sung discloses an anti-corrosion additive for motor fuels containing a minor amount of a short-chain aliphatic alcohol. The anti-corrosion additive is prepared by reacting maleic anhydride and a hydrocarbon substituted mono-primary amine. This reference is primarily concerned with fuel compositions containing minor amounts of short chain alcohols, such as methanol, that have high corrosion activity and which may cause the metallic parts of the fuel system to corrode or rust. This patent does not address the problems associated with wear in fuel pumps caused by a decrease in lubricity of the fuel.
Hutchison et al., in U.S. Pat. No. 4,948,523, discloses a lubricating composition that contains a silver protective agent. The silver protective agent comprises the reaction product of a C.sub.5 -C.sub.60 carboxylic acid and at least one amine selected from the group consisting of: 1) guanidine, urea and thioruea compounds; 2) C.sub.1 -C.sub.20 hydrocarbyl or hydroxy-substituted hydrocarbyl mono-amines, alkylene diamines; and 3) polyalkylene polyamines and N-alkyl glycine. This patent is directed to lubricating oil additives for medium speed diesel engines, such as locomotive engines, which have silver parts in the engine. Large, medium-speed diesel engines often contain silver protected components, such as bearings, and, as such, the lubricating oils may not contain the typical zinc containing wear inhibitors which attack the silver coated parts. This patent does not teach the addition of the lubricity additives of the present invention to fuels or address the lubricity problems associated with modem petroleum based fuels which have low sulfur, polyaromatics and oxygenate content.
U.S. Pat. No. 5,035,720 to Weers discloses a composition for use as a corrosion inhibitor in petroleum based fuels. The composition of Weers is an adduct of a triazole and a basic nitrogen compound selected from polyamines, alkoxyamines, aryloxyamines and monoalkyleneamines. This patent is primarily directed to additives to protect copper and aluminum surfaces of the vehicle fuel system from corrosion.
U.S. Pat. No. 5,336,277 to Poirier et al. discloses a composition for reducing in-tank fuel pump copper commutator wear. Poirier et al. disclose a fuel having an oil soluble triazole-amine adduct and at least one organomercaptan compound which, in combination with a metal deactivator, increases the resistance of the fuel composition to cause copper commutator wear.
An article by Ping et al. entitled: "Comparison of the Lubricity of Gasoline and Diesel Fuels", Society of Automotive Engineers, Inc., (1996), provides a number of test methodologies to measure the friction and wear properties of petroleum based fuels. While this article does not suggest or disclose the presently claimed additives for increasing fuel lubricity, it does provide substantial background on the testing of fuels for lubricity.
While the prior art is replete with numerous treatments for fuels and lubricants, it does not suggest or disclose the present additive that provides adequate lubricity to the fuel and thereby reduce the incidence of fuel pump failure.